The closest living relative of the dinosaurs, these large reptiles are adapted to an aquatic existence. A fold of skin closes the windpipe at the back, so that the animal can open its mouth under water and breathe with its nostrils above the surface. The nostrils, like the eyes and ears, are placed high on the head. When crocodiles are completely submerged, the ears and nostrils are closed by valves, and the eyes covered by membranes. Crocodiles have no salivary glands and usually eat under water. Some species sweep their prey from the land into the water with their powerful, vertically flattened tails. Crocodiles' scales are hard and square, and a few rows of raised scales downt the back and tail contain knobs of bone. There are two families.
There is one species: the gavial or gharial, Gavialis gangeticus which is also known as the true or Indian gavial, it lives in the Indus, Ganges and Brahmaputra rivers systems, feeding on fish. It has very small nasal bones, 27-29 teeth on each side, and a long narrow snout that widens at the nostrils.
Crocodiles: 20 species
Crocodiles live mainly in tropical rivers, though some forms swim out to sea. There are three sub-families. The Alligatorinae sub-family includes the alligators and caymans, which have 17-22 teeth on each side of each jaw; the fourth tooth of the lower jaw fits into a pit in the upper jaw and is invisible when the mouth is closed. In the Crocodylinae, the true crocodiles, with 14 or 15 teeth on each side, the fourth tooth fits into a pit in the upper jaw, but remains visible when the mouth is closed. This tooth is also visible in the Tomistominae, the false gavials; these have 20 or 21 teeth a side.
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